Organic Light Emitting Diode (OLED) devices include a thin film of electroluminescent organic material sandwiched between a cathode and an anode, with one or both of these electrodes being a transparent conductor. When a voltage is applied across the device, electrons and holes are injected from their respective electrodes and recombine in the electroluminescent organic material through the intermediate formation of emissive excitons.
Emissive displays such as OLEDs commonly use anti-reflection films such as circular polarizers to reduce reflection from ambient light caused by the metallic layers of the OLED. A circular polarizer comprised of a linear absorbing polarizer and a ¼ wave film extinguishes a large amount of ambient light incident on the display. This circular polarizer has the disadvantages of absorbing 50% or more of the emitted light from the OLED and also is expensive to produce due the difficulty of applying the ¼ wave film to the linear polarizer since the pass axis of the linear polarizer and the fast or slow axis of the ¼ wave (QW) film must be aligned 45 degrees relative to each other.
The display contrast is defined as the ratio (White−Black)/Black, where White is the brightest on-state and Black is the darkest off-state. In a darkened room, the contrast is limited by the intrinsic Black and White luminance values of the display device. In normal use the ambient light level and the display reflectance add to the intrinsic luminance levels. An ideal circular polarizer (CP) cuts the White state luminance by 50% and it reduces the ambient reflectance to that of the first surface of the polarizer. Because a practical QW element is exact at only one wavelength and only one view angle, hence there is a baseline reflectance.
In a bright ambient environment, such as daylight, the best commercial CP may be insufficient to maintain the required contrast, whereas, in a typical home or office environment the required contrast may be achieved without a high performance CP. The cost of the CP film stack must adjust with the performance value demanded in the intended use.
The display brightness is a key attribute that bears a cost in the expense of electronic drive capacity and its associated bulk as well as the emitter lifetime. In addition, the display power efficiency is an important consumer regulatory counterbalance to display brightness. The CP antireflection stack cuts the brightness and power efficiency by more than half. An anti-reflection component that also enhances brightness adds value.
The CP implementation is complicated by the prescribed 45-degree alignment of the QW and linear polarizer films, which often requires piece to piece lamination rather than roll to roll lamination. An anti-reflection component that enables roll to roll assembly reduces cost.